There have been efforts made to design a valve trim or profile having symmetrically placed notches therein to define a preferred flow path for fluid within the valve. Typical of such efforts are the anti-cavitation trims of the LINCOLNLOG™ valves of Masoneilan/Dresser Industries, Inc. Anti-cavitation trims stage pressure drops through a control valve. These valves have suffered from a number of shortcomings. For example, the notch locations are, at least in some cases, too close to one another to provide proper staging. As a result, fluid within the valve is able to flow from one restriction to the next without utilizing the interstage plenum, as intended, which is necessary to achieve desired staging so as to avoid cavitation. This problem is referred to herein as “short-circuiting.”
Another shortcoming is that these valves, when used with conventional plug tips, do not direct fluid away from the seating surfaces of the plug so as to minimize unbalance forces in the region of the seating surfaces. It would be desirable if the unbalance forces, produced by the fluid pressure drop in the valve, could be reduced, and one manner of reducing the unbalance forces is to minimize the unbalance area in the vicinity of the seating surfaces of the plug.
The manner in which these and other shortcomings are overcome are explained in the following Summary and Detailed Description of the Preferred Embodiments.